1. Field of the Invention
The present invention relates to a power supply temperature sensor and system.
2. Background Art
High voltage batteries, for example, of the type used in hybrid electric vehicles (HEV's), require control and maintenance based on battery temperature. In the case of a high voltage battery system made up of many individual battery cells, the respective temperatures of the cells may vary widely throughout different parts of the battery system. Therefore, it is often desirable to measure the temperature of many different cells to provide a clear picture of the thermal state of the battery system. In order to increase the accuracy of the temperature measurements, it is desirable to measure the temperature as close to the battery cell core as possible, without impairing either the performance or life of the cell.
In order to properly cool a large battery pack made up of many cells, a fan may be used to circulate air across the battery cells to provide convective cooling. The fan may be part of a refrigeration system that provides very cool air to the battery cells to keep them from overheating. In such a case, it is undesirable to have an air conditioning fan blow directly on a battery cell temperature sensor, as this may give an inaccurate temperature reading.
Temperature sensors that are placed close to a battery cell, but not in contact with it, may also give an inaccurate reading of the battery cell temperature. To adjust for this, some systems employ the use of a compensation factor to account for the air space between the temperature sensor and the battery cell. The use of compensation factors, however, cannot always compensate adequately for the measurement inaccuracy. Placing the temperature sensor in direct contact with the battery cell, however, may not be practical in some applications. This is because the high voltage output from the battery cells may damage the low voltage sensor if electrical contact is made between them. In addition, such contact may result in the sensor carrying the high voltage potential to new locations that must also then be protected from the high voltage potential.
Therefore, a need exists for a power supply temperature sensor and system that provides accurate temperature measurements of individual power supply units, such as battery cells, without exposing the temperature sensors to potentially damaging high voltage. Moreover, a need exists to provide temperature sensors that are not unduly influenced by convective cooling currents in the power supply system.